The effect of benzodiazepines on isoniazid induced convulsions, increase of cerebellar cGMP and anterior pituitary cAMP content were compared to the effect of muscimol and nipecotic acid (powerful GABA mimetic compounds). Benzodiazepines like muscimol and nipecotic acid delayed the onset of convulsions induced by isoniazid in doses that did not protect the animals from picrotoxin or strychnine convulsions. Moreover diazepam and muscimol have a similar order of potency in preventing the increase of cerebellar cGMP or pituitary cAMP induced by isoniazid, picrotoxin, harmaline and reserpine. These data suggest that the pharmacological action of benzo-diazepines may be mediated by an effect on GABA neurons.